In electronic photographing technology, developing apparatuses using a two-component developer are used. The developing apparatuses mix a new carrier with toner when the toner is supplied and supply the carrier-mixed toner into a developer accommodation chamber, which ensures a long life of the developer. In addition, the developing apparatuses discharge old developer through a developer discharge hole. For example, JP 2014-115324 discloses a developing apparatus for discharging old developer through a developer discharge hole.